Preoperative fasting plasma C-peptide level may help to predict diabetes outcome after gastric bypass surgery.

BACKGROUND: To evaluate whether preoperative measurement of fasting plasma C-peptide levels is useful to predict diabetes outcome after Roux-en-Y gastric bypass (RYGB) surgery.
MATERIALS AND METHODS: Diabetes outcome after RYGB was evaluated in 126 obese patients: 41 non-diabetic controls (NDC), 29 with impaired glucose tolerance (IGT) and 56 had type 2 diabetes mellitus (T2DM). Body weight, fasting plasma glucose, fasting C-peptide levels, and HbA1c were measured at baseline and 3.6 ± 0.16 years after GBS. Complete resolution of diabetes was defined as: fasting glucose <7.0 mmol/l, HbA1c <6.5 %, achieved without anti-diabetic medication.
RESULTS: Patients with complete resolution of diabetes had a more recent diagnosis of T2DM, lower preoperative HbA1c levels and lower daily doses of metformin and insulin use. These parameters were related to postoperative HbA1c levels but they failed to mark the specific patients who had not reached complete resolution of T2DM. Fasting preoperative C-peptide levels had better predictive power: 90 % of T2DM patients with preoperative fasting C-peptide levels >1.0 nmol/l achieved a postoperative HbA1c <6.5 %, and 74 % achieved complete resolution of their diabetes. In contrast, none of the T2DM patients with a preoperative fasting C-peptide <1.0 nmol/l attained these goals.
CONCLUSIONS: A preoperative fasting plasma C-peptide level <1.0 nmol/l in severely obese T2DM patients indicates partial β-cell failure, and is associated with a markedly reduced chance of complete resolution of T2DM after RYGB. We therefore advocate measuring C-peptide levels in all diabetic patients up for bariatric surgery to improve the prediction of outcome.